Generally, a broadband communication system has limited radio resources. In order to maximize the efficiency of radio resources, a variety of methods for effectively transmitting/receiving signals in a time-, space-, or frequency-domain and their utilization methods have been developed.
Particularly, a multicarrier-based OFDM scheme reduces the complexity of a receiver under frequency selective fading environments of a broadband channel, uses different channel characteristics of subcarriers, and performs selective scheduling in a frequency domain, thereby increasing spectral efficiency. So, the multicarrier-based OFDM scheme has been recently focused to maximize the efficiency of radio resources in the frequency domain.
In order to maximize the efficiency in a space domain, a Multi-Input Multi-Output (MIMO) technology is required, and several time and frequency domains occur in the space domain, so that the multicarrier-based OFDM scheme transmits high-speed multimedia data.
In order to effectively use a time domain, the above-mentioned OFDM scheme performs channel encoding, performs scheduling based on channel selective characteristics of several users, and uses a HARQ scheme appropriate for transmission of packet data.
In order to implement a variety transmission/reception techniques for transmitting broadband Space-Time high-speed packets, transmission of downlink/uplink control signals for time-, space-, and frequency-domains is indispensable.
Under the above-mentioned environments, most conventional arts have been designed to use only radio resources of control channel pre-assigned for transmission of control signals, so that the amount of overhead of the control channels increases under broadband multi-user and multi-antennas environments, thereby reducing RF-channel capacity (e.g., a bandwidth) for actual data.